Yes, holding an action in D&D 5e uses your reaction. When you take the Ready action on your turn, you spend your action to prepare something, then spend your reaction to actually execute it when the trigger occurs. This means readying an action costs both your action and your reaction, making it one of the most expensive choices in the action economy.
How the Ready Action Works
On your turn, you declare two things: a perceivable trigger (“when the goblin steps through the doorway”) and what you’ll do in response (“I attack it”). Your turn then ends. When the trigger happens, you use your reaction to carry out the readied response. If the trigger never occurs before your next turn, nothing happens and both your action and reaction are wasted.
You can also choose to ignore the trigger when it happens. Maybe the situation changed and attacking no longer makes sense. In that case, your reaction stays available, but you’ve still burned your action for the round. The trigger always completes before your reaction activates, so you’re responding to an event, not interrupting it.
Why This Matters for Your Other Reactions
You only get one reaction per round. If you use your reaction to execute a readied action, you can’t also take an opportunity attack, cast a reaction spell like Shield, or use any other reaction-based ability until the start of your next turn. The reverse is also true: if you’ve already spent your reaction on something else (like an opportunity attack), you can’t execute your readied action even if the trigger occurs.
This is the real cost of readying. You’re not just giving up your action for a conditional payoff. You’re also locking out every other reaction you might need. For a spellcaster who relies on Shield or Counterspell, or a melee fighter who values opportunity attacks, that tradeoff can be steep.
Readying a Spell Has Extra Costs
If you ready a spell, you cast it on your turn as normal but hold its energy until the trigger fires. Holding that energy requires concentration, even if the spell doesn’t normally need it. That means if you’re already concentrating on something like Bless or Haste, readying a new spell breaks that concentration.
If you lose concentration before the trigger happens (from taking damage, for example), the spell fizzles but you don’t lose the spell slot. If the trigger simply never occurs, though, the spell slot is gone. You also can’t cast other concentration spells while holding a readied spell, since the held spell is occupying your concentration.
Extra Attack Doesn’t Apply
One of the most common misconceptions about readying is that fighters, rangers, and other martial characters can make multiple attacks with a readied action. They can’t. The Extra Attack feature specifically activates when you take the Attack action on your turn. Readying an attack is the Ready action, not the Attack action, and it resolves on someone else’s turn. Both of those conditions disqualify Extra Attack. You get one swing, period.
This makes readying an attack a significant downgrade for any character with Extra Attack. A 5th-level fighter who readies an attack is dealing roughly half the damage they would on a normal turn. It’s worth doing when timing matters more than damage output, like waiting for an enemy to come into range or coordinating with an ally, but it’s rarely the optimal choice for raw damage.
You Can Ready Movement Instead
The Ready action isn’t limited to attacks and spells. You can also choose to move up to your speed as the readied response. This uses the same framework: you declare a trigger, and when it occurs, you spend your reaction to move. This is useful for situations like following an ally through a dangerous area or retreating when an enemy closes in.
Note that this readied movement replaces your action, not your normal movement. You could still move on your turn before or after taking the Ready action. When the trigger fires, the readied movement then costs your reaction.
Choosing a Good Trigger
Your trigger needs to be a perceivable circumstance, something your character can actually see, hear, or otherwise detect. “When the enemy moves” or “when the door opens” works. “When the enemy thinks about casting a spell” does not, because you can’t perceive thoughts.
The trigger also needs to be specific. You can’t say “when anything happens” as a catch-all. The rules expect something roughly as detailed as the examples in the Player’s Handbook: a creature moving into a doorway, an enemy casting a spell, a chandelier falling. Think of it as a real cause-and-effect decision your character is making in the moment. Most DMs will push back on triggers that are too vague or too broad, and they’re right to do so, since the Ready action is meant to represent a focused, deliberate choice to wait for a particular moment.